Amplifying and reproducing system



May 8, 1934. B. F. MIESS ER 1,958,198

AMPLIFYING AND REPRODUCING SYSTEM Filed July 20, 1929 Patented May 8, 1934 AMPLIFYING AND REPRODUCING SYSTEM Benjamin F. Miessner, Short Hills, N. 3., assignor,

by mesne assignments, to Radio Corporation of America, New York, N. Y., a corporation of Delaware Application July 2-0, 1929, Serial No. 379,674

Claims.

' The present invention relates to amplifying and reproducing systems, particularly such systems employing three electrode vacuum tubes and energizedreproducing devices, and constitutes an improvement over the inventions disclosed in my copending applications, Serial Number 334,870, filed January, 1929 and Serial Number 360,042, filed 3 May, 1929, and in which a filtering system for smoothing out the fluctuations or ripples in a fluctuating source of uni-directional current sup ply system is employed.

One object of my invention is the energizing of the output and input electrodes of three electrode vacuum tubes in amplifying systems with rectified alternating current from the usual commercially available alternating current sources with'little or no resulting hum.

Another object of my invention is to energize the vacuum tubes and the field of the reproducing device in a system from a source of uni-directional fluctuating current while maintaining hum production in the reproducing device low.

A feature of my invention is the employment of the characteristics of three electrode vacuum tubes arranged in push-pull relation or their equivalent as an aid in the filtering operation primarily when functioning in the usual'manner as the output elements of an audio frequency amplifier system. Another feature of my invention is to avoid the use of an excessive amount of bulky and heavy apparatus usual to filter systems employed in connection with the energizing of vacuum tubes from unsteady sources of potential.

Further objects and features of my invention will become apparent as the description of the circuit diagrammatically shown in the accompanying-drawing is developed. Referring to the drawing A designates an antenna connected to ground G through the primary RP1, of a radio frequency transformer RT1, the resonant secondary of which is included in the grid filament circuit of a radio frequency amplifier tube VT1. The plate circuit of tube VT1 contains the primary RP2 of a radio frequency transformer RT2, the resonant secondary of which is contained in the grid-cathode circuit of the detector tube DT, preferably of the indirectly heated cathode type shown. The plate circuit of the detector tube contains the primary AP1 of an audio transformer AT1, the secondary A81 of which is included in the grid-filament circuit of the audio frequency amplifier tube VT2. The plate circuit of the tube VT2 contains the primary Prof a transformer T1 having a split-secondary SS1 and SS2 each contained in the gridfilament circuit of tubes VT3 and VT4 respectively arranged in push-pull relation, and having within their plate circuits the sections SP1 and SP2 of a split primary P2 of an output transformer OT.

The energization of the various tubes is as follows. The source of current is shown as a primary P of a transformer T shunting a source of commercially available alternating current. The transformer T is provided with secondaries S1, S2, S3, S4 and S5. The secondary S1 heats the cathode of the fullwa've rectifier tube FWR, the secondary S2 supplying potential to the anodes thereof. The secondary S3 supplies heating current to the filaments of the tubes VT3 and VT4 connected in parallel. The secondary S4 supplies current to the heater element of the tube DT, and the secondary S5 supplies heating current to the tubes VT1 and VT2 connected in parallel.

In the following description I have deemed it best to describe the function of the tubes VT3 and 1T4 in their position within the filter system first without considering their function as amplifier tubes and then consider their function in the development of audible signals in the loud speaker LS from the signals received upon the antenna A.

In the circuit shown the full-wave rectifier FWR (or a half-wave may be substituted therefor) rectifies alternating current from the source AC with the aid of the transformer T and the secondaries thereof, the output of the rectifier being preferably shunted by a storage and filtering condenser FC1. The uni-directional current may be considered as being consumed by a load resistance LR. To smooth out the ripples in the rectified current I include the plate-filament paths through the tubes VT3 and VTQ, by way of the primaries SP1 and SP2 and the inductance FC, which may be the field coil of the loud speaker unit, an auxiliary choke coil CH1 used merely to supplement the loud speaker field coil should it of itself be insufiicient as a filter choke, series related to the center tap GT2 of the secondary S2. Between the secondaries SS1 and SS2 I have provided a balancing resistance BR through which a negative biasing potential is placed upon the grids of tubes V'I'a and VT; by the variable taps 1 and 2 between the coils FC and CH, the negative potential of these points relative to the filaments of these tubes being caused by the drop in potential across the coil FC due to the plate current fiow of the tubes VTs and VT4 therethrough.

By causing the rectified current from the rectifier to pass through the field coil FC which is shunted by a ripple governing condenser 3, I can develop such pulsating uni-directional potential on the grids of tubes VT3 and VT4, that the amount of filament-to-plate current therethrough can be controlled as well as opposing the ripple therein to any desired degree by the pulsations thus introduced on and controlled at the grids. The inclusion of inductance and resistivity in the coil F0 and the capacity in condenser 3 allows for developing the desired degree of grid biasing potential and controlling for the desired amount and phase of the fluctuation potential on the grid to regulate the amount of current flow through the load resistance LR, and to elimihate ripple therein.

In the event the impedance through the space current path of the tubes VTs and VT4 and the load resistance LR is such that sufficient ripple current cannot be developed on the grids of tubes VTs and VT% to smooth out the load current ripple in the resistance LR to the desired amount, the inclusion of a condenser F02 of variable capacity to provide a lesser impedance for the fluctuating component can be used to advantage. The condenser PCs is employed to prevent actions in the load circuits as represented at LR from being reflected back into the filter system; that is, reaction between the plate circuits of tubes VTi, DI and V'Iz from being reflected back into the rectifier system.

From the foregoing description it will be seen that the plate-filament circuits of the tubes VTl, DT and VT2 can be supplied with substantially constant potential from the terminals 4, 5, of the resistance LR. In the following consideration the terminal 4 may be considered as the high potential of the terminal of the filter system and the terminal 5 may be considered as the low potential terminal thereof, being connected to ground G by the lead 6 as shown.

The plate of the tube VT1 is supplied with current through the primary of radio frequency transformer RT2 and a current limiting resistance R1. This resistance is provided with a bypass condenser 7.

The plate of the detector tube DT is supplied with current from the terminal 4 through a current limiting resistance R2, this resistance likewise being provided with a filter condenser 8. The plate of tube VT2 is connected through the primary P1 of the transformer T1 to the high potential terminal of the system. The proper grid bias potential for the tubes VT1 and VTz is obtained by a biasing resistance BB2 provided with a bypass condenser 12 connected between the lead 6, which is the common grid return of the tubes VT1 and VT2 and the center top of a potentiometer CR1 across the secondary S5 of the transformer T. The heater element of the detector tube DT is maintained at the proper potential relative to its cathode by means of a center tap potentiometer CR2 connected across the secondary S4 of the transformer T, the center tap of the potentiometer being directly connected to the center tap of the potentiometer CR1.

The operation of my device is as follows:

When a radio frequency signal is received upon the antenna A it is transferred to the'grid circuit of tube VT1 through the radio frequency transformer RT1. These radio frequency signals produce a modulation in the plate circuit of the tube VT1 of radio frequency, a path of low impedance to filament thereof being provided through condensers 9 and 10, preferably of equal value, connected between the legs of the filament of the tube VT1 and the lead 6 or ground G. These amplified signals are transferred tothe grid circuit of the detector tube DT, which grid circuit contains the grid-condenser GC and gridleak resistance GL.

The radio frequency currents in the plate circuit of the detector tube are by-passed by means of a condenser 11 and the audio frequency currents are transferred to the grid circuit of tube 'v'Tz in the usual manner for amplification. The tubes VT3 and VTi, having their grid circuits containing the secondaries SS1 and SS2 coupled to the plate circuit of the tube VT2 through the transformer T1, act as usual push-pull amplifiers introducing current into the movable coil MC of the loud speaker LS through the output transformer GT, the primaries SP1 and SP2 of which are connected in the plate circuits of the tubes VT: and VT4 in the manner hereinbefore described.

t will be noted that the resistance LR may be.

omitted when the plate current flow through the tubes JTi, DT and VT2 is equal to the plate current fiow through the tubes VTs and VT4. This arrangement is preferable since the load upon the filter circuit is reduced to a minimum which allows better filtration of fluctuating currents thereby. It will further be noted that with a loud speaker LS having a field coil PC of such a value as to be equal to the combined inductance of the coils FC and CH, the coil CH may be omitted without departing from the spirit of my invention. It is to be understood that detail changes may be made in the circuit set forth in the accompanying drawing, and in particular, changes in the circuits or number of tubes employed as the radio frequency amplifier, detector, and first stage of audio frequency amplifier, as shown in the accompanying drawing without departing from the spirit of my invention.

Having described my invention what I claim is:

1. In an electrical system, the combination of a source of uni-directional pulsating current, a work circuit, and a filter system, said filter system including a pair of thermionically active paths through which current flows to said work circuit, and means influenced by the pulsations in said current for commutating in said electronically active paths the fluctuations out of said Work circuit. l

2. In an electrical system, the combination of a source of uni-directional pulsating current, a work circuit, and a filter system, said filter system including a pair of thermionically active paths through which current fiows to said work circuit, and means influenced by the pulsations in said current for commutating in said electronically active paths the fluctuations out of said work circuit, said means including a loud speaker, the field coil of which is series related between said thermionic paths and one terminal of said source.

3. In an electrical system, the combination of a source of pulsating uni-directional current, a work circuit, a filter system including a pair of three electrode tubes with their space current paths series connected with said work circuit across the terminals of said source, and means through which said pulsating current fiows connected to the grids of each of said tubes for introducing thereon a pulsating potential acting potential acting to neutralize in said tubes pulsations in the current passing therethrough.

4. In an electrical system, the combination of a source of pulsating uni-directional current, a work circuit, a filter system including a pair of three electrode tubes with their space current paths series connected with said work circuit across the terminals of said source, and means through which said pulsating current flows. connected to the. grids of each of said tubes for introducing thereon a pulsating. potential acting to neutralize in said tubes pulsations in the current passing therethrough, said means including a loud speaker, the fieldcoil of which is series related between the space current path of said tubes and oneof the terminals of said source.

5. In. an electrical system, the combination of a. source of. pulsating uni-directional current, a work circuit, a filter system including a pair of three electrode tubes connected in push-pull arrangement with their filament-plate paths in seriesv with said work circuit across the terminals of said source, signal input means within the grid circuit of each of said tubes, output means within the plate circuit of said tubes, and means for developing from said pulsating current controlling potentials for the'grids of said tubes.

6. In an electrical system, the combination of a source of pulsating uni-directional current, a work circuit, a filter system including a pair of three electrode tubes connected in push-pull arrangement with their filament-plate paths in series with said work circuit across the terminals of said source, signal input means within the grid circuit of each. of said tubes, output means within the plate circuit of said tubes, and means for developing from said pulsating current controlling potentials for the grids of said tubes, said means including a loud speaker, the field coil of which is series connected between the filament-plate paths of said tubes and one terminal of said source.

'lfIn an electrical system, the combination of asource of fluctuating uni-directional current, a work circuit energized by said source, a pair of parallel impedances series connected between said source and said work circuit, and means for varying the value of said impedances in consonance with the fluctuating component of said source.

8. In an electrical system, the combination of a source of fluctuating uni-directional current, a work circuit energized by said source, a filter system including a pair of parallel impedances series connected between said source and said work circuit, means for varying the value of each of said impedances at signalling frequency while maintaining the combined impedance substantially constant, and means for varying the value of said combined impedance in consonance with the fluctuating component of said source.

9. In an electrical system, the combination of a source of fluctuating uni-directional current, a work circuit energized by said source, a filter system including a pair of three electrode tubes connected in push-pull arrangement with their filament-plate paths in series with said work circuit across the terminals of said source, means within the grid circuits of said tubes for varying the impedance of said tubes at signalling frequency while maintaining the combined impedance of said tubes substantially constant, and means within the grid-filament circuit of said tubes, and connected between the filament-plate paths of said tubes and one terminal of said source for varying the combined impedance of said tubes in consonance with the fluctuating component of said source whereby the fluctuating potential of said source is isolated from said work circuit.

10. In a receiver for translating radio frequency signals including a radio frequency amplifying system, a detector system and an output system including a pair of amplifying tubes arranged in push-pull relation, said detector system and said output system being connected in cascade, the combination of a source of uni-directionalcurrent of fluctuating potential, the space current paths of at least one of said systems and the space current paths of said pair of amplifying tubes series connected across said source, and means in series between said output system and said source for varying the combined impedance of said amplifying tubes in consonance with the fluctuating potential of said source whereby said fluctuating potentials are isolated from said system preceding said output system and series connected therewith across said source.

11. In a receiver for translating radio frequency signals including a radio frequency amplifying system, a detector system and an output system including a pair of amplifying tubes arranged in push-pull relation, said detector sys tem and said output system being connected in cascade, the combination of a source of uni-directional current of fluctuating potential, the space current paths of at least one of said systems and the space current paths of said pair of amplifying tubes series connected across said source, and means in series between said output system and said source for varying the combined impedance of said amplifying tubes in consonance with the fluctuating potential of said source whereby said fluctuating potentials are isolated from said system preceding said output system and series con nected therewith across said source, said means including a loud speaker, the field coil of which is series connected between the space current path of said output system and said source, and connections between the grids of said amplifier tubes and said field coil at a point removed from the space current paths of said amplifier tubes.

12, In an electrical system the combination of an amplifying system and an output system including a pair of amplifying tubes arranged in push-pull relation, said amplifying system and said output system being connected in cascade, a source of uni-directional current of fluctuating potential, the space current paths of said systems series connected across said source, and means in series between said output system and said source for varying the combined impedance of said amplifying tubes in consonance with the fluctuating potential of said source whereby said fluctuating potentials are isolated from said amplifier system.

13. In an electrical system, the combination of an amplifying system and an output system including a pair of amplifying tubes arranged in push-pull relation, said amplifying system and said output system being connected in cascade, an indicating device including a field winding, a source of uni-directional current of fluctuating potential, the space current paths of said systems series connected across said source, and means in series between said output system and said source for varying the combined impedance of said tubes in consonance with the fluctuating potentials of said source, said means consisting of said field winding and connections between the grids of said tubes and a point on said field winding electrically removed from said output system.

14. In an electrical system, the combination of an amplifying system, and an output system including a pair of amplifying tubes arranged in push-pull relation, said amplifying system and said output system being connected in cascade, a

source of uni-directional current of fluctuating potential, the space current paths of said systems series connected across said source, a choke-coil series connected between said output system and said source, and connections between the grids of said tubes and a point in said choke coil electrically removed from said output system, whereby said fluctuating components of said source are isolated from said amplifying system.

15. In an electrical system, the combination of an amplifying system, and an output system including a pair of amplifying tubes arranged in push-pull relation, said amplifying system and said output system being connected in cas cade, a source of uni-directional current of fluctuating potential, the space current paths of said systems series connected across said source, a choke-coil series connected between said output system and said source, and a low impedance path for the fluctuating components of said source shunting said amplifying system and the space current paths of said amplifying tubes for increasing the fluctuating current fiowing through said choke coil.

16. In an electrical system the combination of a source of power, a pair of tubes arranged in push-pull relation, an indicator having a field coil and a moving element, the filament-plate path of said tubes series connected across said source, means coupling the plate-filament circuit of said tubes to said movable element, and means connecting the grids of said tubes to a point in said field coil electrically removed'irom the filament-plate paths of said tubes whereby the grids of said tubes are maintained at a potential negative to that of said filaments.

17. In an electrical system the combination of a source of power, a pair of tu es arranged in push-pull relation, an indicator having a field coil and a moving element, the filament-plate path of said tubes series connected across said source, means coupling the plate-filament circuit of said tubes to said movable element, and means connecting the grids of said tubes to a point in said field coil electrically removed from the filament-plate paths of said tubes whereby the grids of said tubes are maintained at a potential negative to that of said filaments, said means including a balancing resistor for the grids of said tubes.

18. In an electrical system the combination of a source of power, a pair of tubes arranged in push-pull relation, an indicator having a field coil and a moving element, the filament-plate path of said tubes series connected across sald source, means coupling the plate-filament circuit of said tubes to said movable element, and means connecting the grids of said tubes to a point in said field coil electrically removed from the filament-plate paths of said tubes whereby the grids of said tubes are maintained at a potential negative to that of said filaments, said means including a transformer having a split secondary, and a balancing resistor series connected between the sections of said secondary.

19. In a radio receiving system which includes an amplifying network a portion of which comprises a pair of electronic tubes connected in push-pull, a power supply circuit for said system including a source of pulsating direct current, a filter circuit having input terminals and output terminals said filter circuit including the space paths of said push-pull connected thermionic tubes, means for connecting said source of pulsating direct current to the input terminals of said filter circuit, a load circuit includ ing at least. another portion of said amplifier network, said load circuit being connected to the outputterminals of the filter circuit and means influenced by the pulsations in the current from said source for varying the impeding characteristics of the space paths of the pushpull tubes in such phase as to oppose the effect of the pulsations in said current on the load.

20. In a radio receiving system including a radio frequency. amplifier, a detector stage and an audio frequency amplifier, said audio frequency amplifier comprising a pair of electronic tubes connected in push-pull, a reproducer including a field coil, a power supply circuit for said system including a source of pulsating direct current energy, a filter circuit having input terminals and output terminals, said filter circuit including the space paths of said push-pull connected tubes and the field coil of said reproducer in series, means for connecting said source of pulsating direct current to the input terminals of said filter, a load circuit including at least said radio frequency amplifier and detector stage connected to said filter output terminals and means influenced by the pulsations in the current from said source for varying the resistance of the space paths of said push-pull connected tubes in a sense to neutralize the effect. of the pulsations in said current on the load.

BENJAMIN F. MIESSN ER. 

